Efficient and cost effective spray cooling of electronic assemblies requires high-density system packaging. However, the density of the design leads to heat removal problems caused by liquid and vapor leaving the surfaces of integrated circuits (chips) interfering with and disrupting the sprays which are directed at the surfaces of the same and other chips. Liquid and vapor leaving one chip can cause poor heat-transfer performance in adjacent chips. This is particularly likely to occur in the very common circumstance where a high-powered chip, requiring a large volume flux of spray, is adjacent to one or more lower-powered chips requiring less spray volume. Fluid coating the high-powered chip's surface absorbs heat and leaves as a mixture of liquid and gaseous vapor. The volume and velocity of this fluid movement can be considerable, and due to lack of control over its direction and movement, it is particularly likely that it will interfere with the spray directed at adjacent chips. This interference can cause flooding of the device which inhibits thin film evaporation, thereby reducing the heat transfer performance. This can result in overheating of these adjacent chips.
One possible solution is to increase the spray volume directed at lower-power chips. This solution is flawed for several reasons. First, excess coolant carried on the surface of the lower-powered chips can actually reduce the quantity of coolant which undergoes a heat-absorbing phase-change. Where more than a thin film is used to cover a heat generating component the rate of heat transfer is reduced. Secondly, the cumulative effect of an increased spray volume directed by several spray nozzles at several low-powered chips surrounding a high-power chip could result in undesired changes in the spray pattern directed at the high-powered chip. Thirdly, excessive spray requirements necessarily result in a requirement of greater pump capacity, overall greater coolant supply and an associated increase in costs. And finally, since the overall heat produced by the entire system can result in the vaporization of only a fixed quantity of liquid coolant, significantly exceeding that level of coolant supplied will result in a significant excess quantity of liquid coolant. In some applications, the spray module may tend to fill up with liquid. If this coolant is not properly directed, it could swamp chips in its flow pathway, thereby covering such chips with more than the optimal quantity of coolant for maximum efficiency in heat transfer.
A similar possible solution is to employ overlapping sprays to suppress the interference effect. However, in most applications the chips are not spaced in a manner that supports this strategy without unduly increasing the system flow rate requirements resulting in the above problems.
A further possible solution to the problem of interference between the spray directed at adjacent chips is to design the board in a manner in which minimization of this phenomena is a design parameter. However, this significantly increases design costs. More troubling still, it is possible that no arrangement of the chips on the board may result in a satisfactory design in many applications. Also, the design engineer and board layout technician may not be well-versed in thermal issues, and may be unable to achieve satisfactory results.
For the foregoing reasons, there is a need for a fluid control apparatus and method of use that can result in enhanced control over the direction and distribution of spray coolant in a manner that reduces or eliminates the interference caused by spray directed at a first chip with the spray and cooling process of a second chip.